As shown in FIG. 5, a bush 50 of a bearing, especially of a dry bearing, has a cylindrical shape, and the inner surface of the bush 50 serves as a bearing surface 51 having a good sliding-contact property. The bush 50 is fixed on the inner surface of a housing H, and rotatably supports a rotary shaft S inserted in the bearing surface 51.
The rotary shaft S supported by the bearing surface 51 of the bush 50 has a diameter slightly smaller than an inner diameter of the bearing surface 51 so that the rotary shaft S rotates smoothly, and a clearance .delta. exists between the rotary shaft S and the bearing surface 51 of the bush 50. Consequently, if foreign matters such as dust enter into the clearance .delta. from the outside, they will damage the bearing surface 51. In order to prevent foreign matters from entering into the clearance, conventionally, seal rings 52 are attached to both ends of the bush 50 so as to seal the clearance .delta..
Also, in an invention disclosed in JP-U-55-181064, seal rings are secured on a rotary shaft, to thereby seal the clearance .delta..
In those conventional ways, however, sealing is effected with the seal rings 52 which are separate members attached to both sides of the bush 50. Therefore, an extra cost is required in producing such separate seal ring 52, and also, there arises a problem that assembling operation of the rotary shaft S to the bush is rather complicated.